RGx1 Does each member of our party need a Half Fare Travelcard?
Basically you could also get 4 additional half fare tickets for the Swiss part of that railway journey (probably Domodossola to Geneva), as two half fare tickets for the same person / route are considered as a valid full fare ticket.
A Swiss Half Fare Card makes only sense if the total ticket costs of your entire stay in Switzerland would exceed 300.- full fare (or 150.-) half fare per person.